Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on murine heart development: alteration in fetal and postnatal cardiac growth, and postnatal cardiac chronotropy.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related chemicals are potent cardiovascular teratogens in developing piscine and avian species. In the present study we investigated the effects of TCDD on murine cardiovascular development. Pregnant mice (C57Bl6N) were dosed with 1.5-24 microg TCDD/kg on gestation day (GD) 14.5. At GD 17.5, fetal mice exhibited a dose-related decrease in heart-to-body weight ratio that was significantly reduced at a maternal dose as low as 3.0 microg TCDD/kg. In addition, cardiocyte proliferation was reduced in GD 17.5 fetal hearts at the 6.0-microg TCDD/kg maternal dose. To determine if this reduction in cardiac weight was transient, or if it continued after birth, dams treated with control or 6.0 microg TCDD/kg were allowed to deliver, and heart weight of offspring was determined on postnatal days (P) 7 and 21. While no difference was seen on P 7, on P 21 pups from TCDD-treated litters showed an increase in heart-to-body weight ratio and in expression of the cardiac hypertrophy marker atrial natriuretic factor. Additionally, electrocardiograms of P 21 offspring showed that the combination of in utero and lactational TCDD exposure reduced postnatal heart rate but did not alter cardiac responsiveness to isoproterenol stimulation of heart rate. These results demonstrate that the fetal murine heart is a sensitive target of TCDD-induced teratogenicity, resembling many of TCDD-induced effects observed in fish and avian embryos, including reduced cardiocyte proliferation and altered fetal heart size. Furthermore, the combination of in utero and lactational TCDD exposure can induce cardiac hypertrophy and bradycardia postnatally, which could increase the risk of cardiovascular disease development.     

Mortality in dioxin-exposed mice infected with influenza: mitochondrial toxicity (reye's-like syndrome) versus enhanced inflammation as the mode of action.

Increased mortality following influenza A infection was reported in B6C3F1 mice exposed to a low (0.01 micro g/kg) dose of dioxin. However, mortality was not associated with increased viral load and antibody titers to the virus were not decreased at doses of TCDD < or = 10 micro g/kg, suggesting that viral overgrowth, secondary to immunosuppression, was not the proximate cause of death. We tested the hypothesis that mitochondrial toxicity and dysfunction, similar to Reye's syndrome (RS) in humans, is responsible for increased mortality in dioxin-exposed, infected B6C3F1 female mice, based on similarities in the biochemical and immunological events that occur in RS and in TCDD-exposed animals. Endpoints were also included to test the hypothesis that increased pulmonary inflammation following dioxin exposure, in the absence of mitochondrial toxicity, was associated with increased mortality. Dose-related effects of TCDD alone, infection with influenza A alone, and combined TCDD exposure/influenza infection were evaluated. Mice were given a single ip injection of 0, 0.001, 0.01, 0.1, or 1.0 micro g TCDD/kg, 7 days before infection by intranasal instillation of an estimated LD(10-20) of influenza A Hong Kong/8/68 (H3N2) and were terminated 1, 7, and 10 days after infection. Serum, bronchoalveolar lavage fluid (BALF), and lung tissue were collected for various measurements, including clinical chemistries, cell counts, cytokine analysis, and viral titers. Exposure to < or = 1.0 micro g TCDD/kg did not increase mortality; virus titers were similar at all doses of TCDD and there was no dioxin-related effect on serum NH(3) or glucose concentrations, two prominent indicators of the altered mitochondrial oxidative metabolism typically observed in RS. A study was therefore conducted over a wider range of TCDD doses. A single injection of 0, 0.025, 0.5, or 10 micro g TCDD/kg preceded infection by 7 days; subgroups of noninfected control and highest dose group (10 micro g TCDD/kg) mice were also evaluated for biochemical and immunological endpoints on the equivalent of infection day 4 to provide baseline data. Five days after infection the same endpoints described above were evaluated. The 10 micro g TCDD/kg dose increased mortality, but once again did not increase virus titer; as in previous experiments, serum biochemistry endpoints did not support mitochondrial dysfunction. These results suggest that RS is an unlikely explanation for increased influenza mortality in TCDD-exposed mice. Rather, constituents in BALF implicate increased pulmonary inflammation as the mode of TCDD action.     

Effect of a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin on immune function in male NC/Nga mice.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces immunosuppression in humans and animals. However, the effect of TCDD on Th2-type immune responses such as allergic reactions has been unclear. Using NC/Nga mice that developed atopic dermatitis-like skin lesions with marked elevation in plasma of total IgE when bred under conventional conditions, we investigated the effects of a single oral dose of TCDD on immune responses. NC/Nga mice received a single oral dose (0 or 20 microg/kg body weight) of TCDD. On day 7, treatment with TCDD alone decreased the cellularity of thymus. However, treatment with TCDD modified the cellularity of spleens and mesenteric lymph nodes (MLNs) but not of the thymus on day 28. When NC/Nga mice received ip immunization with OVA and alum on the same day as the TCDD treatment (0, 5, or 20 microg/kg body weight), TCDD markedly suppressed the concentrations of Th2-type cytokines (e.g., IL-4 and IL-5) in culture supernatants of spleen cells, whereas IFN-gamma production significantly increased. TCDD exposure reduced anti-OVA and total IgE antibody titers in plasma and did not induce the development of atopic dermatitis-like lesions in the pinnae or dorsal skin of NC/Nga mice. These results suggest that in NC/Nga mice, exposure to TCDD may impair the induction of Th2-type immune responses.     

Effect of prenatal exposure to TCDD on the promotion of endometriotic lesion growth by TCDD in adult female rats and mice.

Several lines of research led to our hypothesis that perinatal exposure to TCDD may alter the sensitivity of adult rodents to the promotional effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on endometriosis. Pregnant rats and mice were treated on gestation day (GD) 8 with either 1 (rats) or 3 (mice) microg TCDD/kg or vehicle. Female offspring were reared to adulthood, and endometriosis was induced surgically. All animals received 0, 3, or 10 microg TCDD/kg 3 weeks prior to surgery, at the time of surgery, and 3, 6, and 9 weeks after surgery. Necropsies were performed 12 weeks after surgery. Measurements at necropsy included the diameter of endometriotic lesions and body, uterine, ovarian and liver weights. While no effect of treatment on lesion diameter was found in rats, analyses revealed that perinatal plus adult exposure to TCDD can increase the size of endometriotic lesions surgically induced in mice. These and additional data on body and organ weights are consistent with previous work. These data confirm the sensitivity of mice to the promotion of endometriotic lesion growth by TCDD and indicate a perinatal effect of TCDD on this parameter when perinatal exposure on GD8 is supplemented with adult exposure to TCDD of female mice.     

Effect of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on Pulmonary Influenza Virus Titer and Natural Killer (NK) Activity in Rats

Suppression of immune function and enhanced susceptibility toinfection in mice is one of the more sensitive indicators ofTCDD toxicity. Recent efforts to demonstrate similar effectsin the rat have shown that there are considerable differencesbetween the two species. The purpose of this study was to determinethe effect of TCDD exposure on (a) an influenza virus host resistancemodel in rats and (b) natural killer cell activity in the lungand spleen. Fischer 344 rats were treated with 10 µg TCDD/kgbody weight via gavage and infected intranasally with rat-adaptedinfluenza virus (RAIV) 7 days later. Virus-augmented NK activityassessed at 48 hr postinfection in the lung was significantlysuppressed in rats treated with 3, 10, or 30 µg TCDD/kgbody weight. Spontaneous NK activity in either lung or spleenwas not affected by TCDD exposure. Significantly higher virustiters were observed on Days 2, 3, and 4 postinfection in thelungs of rats treated with TCDD (10 µg/kg) TCDD had noeffect on the amount of virus recovered from nasal lavage. Acuteexposure to TCDD did not significantly affect lung and bodyweights in rats infected with RAIV except in the highest dose(30 µg/kg) treated rats. Rats exposed to repeated dosesof TCDD showed a significant increase of lung weights and L/Bratios when rats were infected with RAIV after TCDD exposure.Virus-augmented pulmonary NK activity in these rats was significantlysuppressed; however, the suppression was not more profound thanthat in rats exposed to a single dose of TCDD. However, an increaseof lung weights and lung/body weight ratios was observed inRAIV infected rats which were exposed to repeated doses of TCDD(cumulative dose of 10 µg/kg). Virus-augmented NK activitywas significantly sup pressed in rats exposed to repeated dosesof TCDD. Our results showed that TCDD suppressed virus-augmentedpulmonary NK activity and this effect may at least in part berelated to enhanced susceptibility of rats to influenza virus.     

In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure: effects on fetal and adult cardiac gene expression and adult cardiac and renal morphology.

The mouse heart is a target of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during fetal development, and microarray analysis demonstrates significant changes in expression of cardiac genes involved in extracellular matrix (ECM) remodeling. We tested the hypothesis that developmental TCDD exposure would disrupt cardiac ECM expression and be associated with changes in cardiac morphology in adulthood. In one study, time-pregnant C57BL/6 mice were dosed with corn oil or 1.5, 3.0, or 6.0 microg TCDD/kg on gestation day (GD) 14.5 and sacrificed on GD 17.5, when changes in fetal cardiac mRNA expression were analyzed using quantitative PCR. TCDD induced mRNA expression of genes associated with ECM remodeling (matrix metalloproteinase 9 and 13, preproendothelin-1 [preproET-1]), cardiac hypertrophy (atrial natriuretic peptide, beta-myosin heavy chain, osteopontin), and aryl hydrocarbon receptor (AHR) activation (cytochrome P4501A1, AHR repressor). Further, all TCDD-induced changes required the AHR since gene expression was not altered in AHR knockout fetuses. In a second study, time-pregnant mice were treated with corn oil or 6.0 microg TCDD/kg on GD 14.5, and male offspring were assessed for changes in cardiac gene expression and cardiac and renal morphology at 3 months. All TCDD-induced changes in cardiac gene expression observed fetally, except for preproET-1, remained induced in the hearts of adult male offspring. Adult male offspring of TCDD-exposed dams also displayed cardiac hypertrophy, decreased plasma volume, and mild hydronephrosis. These results demonstrate that in utero and lactational TCDD exposures alter cardiac gene expression and cardiac and renal morphology in adulthood, which may increase the susceptibility to cardiovascular dysfunction.     

Examination of immune parameters and host resistance mechanisms in B6C3F1 mice following adult exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Adult female B6C3F1 mice were given a single ip dose of 0, 01, 1.0, or 10.0 micrograms/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and examined for immune function and host resistance 7-10 d later. Exposure to TCDD resulted in a significant dose-related decrease in induction of both IgM and IgG antibody-forming cells. This suppression was noted for both T-dependent and T-independent antigens. TCDD at a dosage of 10 micrograms/kg was shown to suppress production of antibody to viral hemagglutinin. In contrast, TCDD exposure had no significant effect on natural killer cell function, production of interferon, or various parameters of macrophage function. Assessment of host resistance revealed a significant increase in susceptibility to fatal infection with influenza virus, but no significant alteration in susceptibility to infection with the bacterium Listeria monocytogenes.     

Examining the relationship between impaired host resistance and altered immune function in mice treated with TCDD

Exposure to TCDD suppresses the immune response to numerous antigens, including bacterial and viral pathogens. Although we administer a non-lethal infection with influenza A virus, we often observe significant mortality in TCDD-treated animals. With the goal of identifying which TCDD-induced defects impair host resistance, we conducted a dose response study to examine whether alteration of particular immunological endpoints could be correlated with mortality. C57Bl/6 mice were treated with vehicle control, or 1, 2.5, 5, 7.5 or 10 microg/kg TCDD 1 day prior to intranasal (i.n.) infection with influenza virus. Survival was monitored for 9 days, when remaining mice were sacrificed and multiple endpoints evaluated. Lymphocyte migration to the lung and the production of virus-specific IgG2a, IgG1, and IgG2b antibodies were significantly diminished, even at the lower doses. IgA was enhanced in all groups treated with TCDD. In contrast, T cell expansion in the lymph node, and the production of IFNgamma and IL-12 were relatively resistant to suppression. Treatment with TCDD also enhanced pulmonary neutrophilia in infected mice. These results suggest that decreased antibody production and hyperinflammation may contribute to the death of TCDD-treated mice, and underscore the importance of evaluating numerous endpoints before concluding that a chemical is or is not immunotoxic.     

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suppresses the humoral and cell-mediated immune responses to influenza A virus without affecting cytolytic activity in the lung.

The immune response to influenza virus is exquisitely sensitive to suppression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD); however, the cellular mechanisms underlying the suppressive effects of TCDD are unknown. Mice exposed to TCDD exhibited a dose-responsive increase in mortality following an otherwise non-lethal influenza virus infection. Given that cytotoxic T lymphocytes (CTL) are generally thought to resolve primary infections in the lung, we tested the hypothesis that exposure to TCDD suppresses T-cell responsiveness, leading to decreased CTL in the lung. After infection with influenza virus, naive CD8+ lymphocytes are activated and differentiate in the mediastinal lymph node (MLN). In mice exposed to TCDD and infected with influenza virus, the number of CD8+ MLN cells was reduced 60% compared to vehicle-treated mice. Moreover, MLN cells from TCDD-treated mice failed to develop cytolytic activity, and the production of interleukin (IL)-2 and interferon (IFN)-gamma was suppressed. Exposure to TCDD also altered the production of virus-specific antibodies, decreased the recruitment of CD8+ cells to the lung, reduced the percentage and number of bronchoalveolar lavage cells bearing a CTL phenotype (CD8+CD44hiCD62L(l) degrees ), and suppressed IL-12 levels in the lung. Despite our findings that exposure to TCDD suppressed T cell-dependent functions, the cytolytic activity of lung lavage cells from TCDD and vehicle treated mice was equivalent, and IFN gamma levels in the lungs of mice treated with TCDD were enhanced 10-fold. Thus, while exposure to TCDD suppressed a number of responses associated with the development of adaptive immunity to influenza virus, a direct link between these effects and enhanced susceptibility to influenza remains unclear.     

Acute administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in pregnant Long Evans rats: association of measured tissue concentrations with developmental effects.

Prenatal exposure to TCDD interferes with fetal development at doses lower than those causing overt toxicity in adult animals. Exposure to TCDD during development produces alterations in the reproductive system of the developing pups- delayed puberty and reduced sperm counts in males and malformations in the external genitalia of females. The objectives of this study were to determine maternal and fetal tissue concentrations of TCDD after acute exposure and whether these tissue concentrations can be used to estimate the intensity of the developmental abnormalities reported by other laboratories. Pregnant Long Evans rats received a single, oral dose of 0.05, 0.20, 0.80, or 1.0 microg [3H]-TCDD/kg on gestation day (GD) 15, and maternal and fetal tissue concentrations of TCDD were measured on GD16 and GD21. On GD16, maternal liver contained the greatest amount of TCDD (30-47% administered dose). One day after administration of 0.20 microg TCDD/kg on GD15, there were 13.2 pg TCDD/g present in an individual fetus. This concentration is associated with delayed puberty and decreased epididymal sperm counts in male pups as well as malformations in the external genitalia of females. For the responses studied, tissue concentration measured during a critical period of gestation adequately predicts the intensity of the response. In addition, there was a strong correlation between fetal body burden and maternal body burden on GD16. A dose of 0.05 microg TCDD/kg resulted in maternal body burdens of 30.6+/-3.1 and 26.6+/-3.1 ng TCDD/kg on GD16 and GD21, respectively. In conclusion, low-level TCDD exposure during the perinatal stage of life can produce adverse effects within the developing pups and that tissue concentration measured during a critical period is the appropriate dose metric to predict adverse reproductive and developmental effects.     

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on molar and mandible traits in congenic mice: a test of the role of the Ahr locus

2,3,7,8-Tetracholorodibenzo-p-dioxin is a highly toxic substance that can cause a variety of adverse effects on organisms. While it has been shown that TCDD acts mainly through the aryl-hydrocarbon receptor (AHR), the mechanism of toxicity is not completely clear. To test the role of the AHR in mediating the effects of TCDD, we exposed two congenic strains of mice differing only at the Ahr locus (Ahr(b)/Ahr(b) and Ahr(d)/Ahr(d)) to TCDD (0, 0.01, 0, or 1 microg/kg body weight) in utero on gestation day 13 and examined the developmental effects on mandible and mandibular tooth row size and shape. Our hypothesis was that TCDD would significantly affect one or more of these endpoints in Ahr(b)/Ahr(b) mice, previously shown to be sensitive to the effects of TCDD, while causing little or no effect in mice carrying the less sensitive Ahr(d) allele. At the doses used in this study, TCDD did not alter the size of mandibles or molars in either Ahr(b)/Ahr(b) or Ahr(d)/Ahr(d) mice. However, we did find that the highest dose of TCDD altered mandible shape, but only in Ahr(b)/Ahr(b) (not Ahr(d)/Ahr(d)) male mice. Similarly, the highest dose of TCDD significantly altered molar shape in Ahr(b)/Ahr(b) but not Ahr(d)/Ahr(d) male mice, although females in both congenic strains were affected. These results suggest that the effects of TCDD on molar and mandible shape are influenced by the Ahr genotype but that males and females differ in sensitivity to both of these effects.     

Effect of low-dose 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on influenza A virus-induced mortality in mice.

Dioxins, including the most toxic congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), exert diverse biological effects in humans and animals. Host resistance, especially to virus infections, is considered one of the most sensitive targets of TCDD-toxicity, while a recent study showed that the vulnerability to TCDD of host resistance to viruses varied form experiment to experiment. Burleson et al. [Fundam. Appl. Toxicol. 29 (1996) 40] reported that a single oral dose as low as 10 ng TCDD/kg increased the mortality of mice infected with influenza A virus. If this value had been adopted as the basis for the tolerable daily intake (TDI) of dioxins, the TDI of 1-4 pg toxic equivalent (TEQ)/kg per day recommended by WHO would have to be lower. In the present study, we used the same experimental protocol described by Burleson et al. to determine whether low-dose TCDD consistently compromises the host resistance of mice infected with influenza A virus. To do so, we investigated the effect of TCDD in the dose range of 0-500 ng/kg on the mortality of virus-infected female B6C3F1 mice. We also investigated the sex- and strain-dependency of host resistance in male B6C3F1 mice and in female C57Bl/6, Balb/c, and DBA/2 mice by administering the same dose range of TCDD. The results showed that TCDD doses up to 500 ng/kg did not increase the mortality of virus-infected mice in any of the strains. Further studies on the mechanism underlying the toxicity of TCDD are needed to assess the risk of exposure to this compound in influenza A virus infection.     

Effect of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on Influenza Virus Host Resistance in Mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes numerous immunotoxiceffects including thymic involution and an immunosuppressionof nonspecific as well as specific cell- and humoralmediatedimmunity. TCDD administration to laboratory animals also resultsin a decreased resistance to numerous bacteria, viruses, andparasites. Effects on virus host resistance appear to be amongthe most sensitive effects of TCDD immunotoxicity. However,previous studies have not achieved a no effect level. The presentstudies utilized an influenza virus host resistance model inmice to quantify the sensitivity of this model to TCDD and todetermine the NOAEL (no observed adverse effect level) of TCDDfor influenza virus. Results indicated that a single dose ofTCDD at 0.10, 0.05, or 0.01 µg/kg resulted in an increasedmortality to Hong Kong influenza virus when mice were challenged7 days after TCDD administration. Increased mortality was notcorrelated with increased virus titers in the lungs. TCDD at0.005 or 0.001 µg/kg had no effect on influenza-inducedmortality. TCDD alone did not affect thymus weight at any doseadministered in this study. TCDD also did not alter the virus-enhancedincrease in lung weight:body weight ratio nor the virus-induceddecrease in thymus weight. Thus, low levels of TCDD exposurelead to enhanced mortality to influenza virus; however, themechanism of this effect remains to be elucidated. Nonetheless,enhanced mortality to influenza virus in mice following a singledose of 10 ng TCDD/kg represents the most sensitive adverseeffect yet reported for TCDD.     

Persistent suppression of delayed-type hypersensitivity in adult F344 rats after perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Recently we observed a suppressed delayed-type hypersensitivity (DTH) response to bovine serum albumin (BSA) in the 4-5-month-old offspring of F344 rat dams receiving as little as 1.0 microg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg on gestational day (GD) 14. This study was designed to characterize better this suppression of the DTH response. First, the persistence of the DTH suppression was determined by measuring the DTH response to BSA in the offspring of dams dosed orally with 3.0 microg TCDD/kg on GD14 as well as in age-matched controls at 4, 8, 12 and 19 months of age. TCDD significantly suppressed the males' DTH response through 19 months of age. While the females' DTH response was reduced at 8, 12 and 19 months, significant suppression was observed only at 4 months of age. Secondly, the lowest maternal dose of TCDD that produced DTH suppression was determined by measuring the DTH response to BSA in the 4- and 14-month-old offspring of dams dosed orally with 0, 0.1, 0.3 or 1.0 microg TCDD/kg on GD14. In the males, suppression was observed at a maternal dose as low as 0.1 microg TCDD/kg at 14 months of age, while a maternal dose of 0.3 microg TCDD/kg was necessary to cause suppression in the 14-month-old females. Both males and females were more sensitive to the suppression at 14 months of age than at 4 months of age. Lastly, the DTH response to a second antigen was examined by measuring the DTH response to either BSA or keyhole limpet hemocyanin (KLH) in the 5- or 4-month-old male offspring, respectively, of dams dosed orally with either 0 or 3.0 microg TCDD/kg on GD14. The DTH response to both antigens was suppressed significantly. Phenotypic analysis was performed on thymus and lymph node suspensions. Significant effects in the thymus included an increased percentage of gammadelta TCR+ cells and a decreased percentage of gammadelta TCR+/CD4- CD8- and MHCI- MHCII- cells. In the popliteal lymph node draining the BSA-injected footpad, there was a decreased percentage of gammadelta TCR+ and MHCI- MHCII- cells and an increased percentage of MHCI+ cells. In conclusion, the suppression of the DTH response associated with perinatal TCDD exposure is persistent through late adulthood, occurs at a low dose (i.e. 0.1 microg TCDD/kg) to the dam, and is more pronounced in males than females. While phenotypic analysis identified differences in subsets of thymocytes and lymph node cells between control and TCDD exposed offspring, no clear correlations were established between altered subpopulations and suppressed DTH responses.     

The effect of perinatal TCDD exposure on caries susceptibility in rats.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the model compound of polychlorinated dibenzo-p-dioxins and furans, is a potent toxicant with the ability to hamper development. Accidental exposure to TCDD has been linked with various developmental dental aberrations in humans, and experimentally it has been shown that TCDD causes, among other defects, hypomineralization of dental hard tissues in rodents. Here, we studied the effect of very low perinatal TCDD exposure on dental caries susceptibility and mineral composition of tooth enamel in rats. Pregnant line C rats (rat line developed in our laboratory) were dosed 0.03-1.0 microg/kg TCDD on gestation day 15 and allowed to give birth and nurse until weaning on postnatal day 21. The offspring were challenged with cariogenic treatment including sugar-rich diet and three inoculations with Streptococcus mutans. Control groups involved animals with or without cariogenic challenge or TCDD treatment. The number of caries lesions in left lower molars was determined by Schiff's staining after 8 weeks of weaning. TCDD treatment increased cariogenic lesions in the enamel at the lowest maternal dose used, 0.03 microg/kg, and at the highest maternal dose, 1 microg/kg, the lesions extended through the enamel to dentin more frequently. Changes in mineral composition measured by electron probe microanalyzer, scanning electron microscopy, and energy-dispersive spectrometry could not explain the increased caries susceptibility. In conclusion, perinatal TCDD exposure can render rat molars more susceptible to caries.     

Oxidative stress in female B6C3F1 mice following acute and subchronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly persistent trace environmental contaminant and is one of the most potent toxicants known to man. Hassoun et al. (1998, Toxicol. Sci. 42, 23-27) reported an increase in the production of reactive oxygen species (ROS) in the brain of female B6C3F1 mice following subchronic exposure to TCDD at doses as low as 0.45 ng/kg/day. In the present study, oxidative stress was characterized in liver, spleen, lung, and kidney following subchronic (0.15-150 ng/kg; 5 days/week for 13 weeks, po) or acute exposure (0.001-100 microg/kg, po) to TCDD in order to investigate the interaction between tissue concentration and time for production of ROS. Seven days following acute administration of TCDD, mice were sacrificed; they demonstrated increases in liver superoxide anion production (SOAP) and thiobarbituric acid reactive substances (TBARS) at doses of 10 and 100 microg/kg, associated with hepatic TCDD concentrations of 55 and 321 ng/g, respectively. Liver obtained from mice following subchronic TCDD exposure demonstrated an increase in SOAP and TBARS above controls at doses of 150 ng/kg/day with liver TCDD concentration of only 12 ng/g. Interestingly, glutathione (GSH) levels in lung and kidney following sub-chronic TCDD exposure were decreased at the low dose of 0.15 ng/kg/day. This effect disappeared at higher TCDD doses. The data suggest that higher tissue TCDD concentrations are required to elicit oxidative stress following acute dosing than with subchronic TCDD exposure. Therefore, the mechanism of ROS production following TCDD exposure does not appear to be solely dependent upon the concentration of TCDD within the tissue. In addition, very low doses of TCDD that result in tissue concentrations similar to the background levels found in the human population produced an effect on an oxidative stress endogenous defense system. The role of this effect in TCDD-mediated toxicity is not known and warrants further investigation.     

Fewer T lymphocytes and decreased pulmonary influenza virus burden in mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The immune system is a sensitive target for the toxicity of the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In mice, immunotoxicity associated with exposure to TCDD includes suppression of humoral and cell-mediated immunity and impaired host resistance to infectious agents. However, the underlying mechanisms for these effects of TCDD are unknown. We previously reported that treatment of C57BI/6 mice with TCDD and influenza A virus increases mortality, impairs cytokine production, and suppresses T cell expansion and the generation of cytotoxic T lymphocytes (CTL) in the draining lymph node. However, the overall virus-specific cytolytic activity in the lung is unaffected. This enigmatic finding left several questions unanswered, including whether decreased CD8+ lymphocytes in the lung are the consequence of either delayed or suppressed recruitment of cells to the lung; whether exposure to TCDD affects the recruitment of CD4+ cells to the lung; and what effect TCDD treatment has on pulmonary virus burden. To compare the kinetics of the response in vehicle- and TCDD-treated mice, we examined the number of bronchoalveolar lavage (BAL) cells and CTL activity in the lung through d 10 postinfection. We found that the peak day for cellular influx and cytolytic activity in the lung is 9 d after infection. Immunophenotypic analysis of BAL cells shows that, when compared with BAL cells from infected controls, exposure to TCDD caused a 50% decrease in the percentage and number of both CD4+ and CD8+ cells. When the pulmonary virus burden was examined over time, we found that on d 1-5 postinfection, lungs from mice exposed to TCDD generally had lower virus titers than lung homogenates from vehicle-treated controls. By d 9 postinfection, no influenza virus was detected in lung homogenates from either vehicle- or TCDD-treated mice. These findings are likely not related to the observed decrease in CD4+ and CD8+ BAL cells; moreover, the diminished CD4+ population in the lung indicates that CD4+ cells are probably not compensating for the decreased CTL generation in TCDD-treated mice. Our observation that mice exposed to TCDD and infected with influenza virus do not have an increased pulmonary virus burden suggests either that TCDD treatment alters the host response to infection, creating a cellular environment that is less supportive for viral growth, or that exposure to TCDD directly affects influenza virus, leading to impaired virus replication within lung epithelial cells.     

Low Concentration of a Dioxin (2, 3, 7, 8 TCDD) Affects the Glycosidases and Acid Phosphatase Activity in Mice Hepatocytes

Present communication reports the effects of environmentally available, low doses of tetra chloro di benzo-p-dioxin (2,3,7,8 TCDD) to lysosomal enzymes in mice liver. The study tests the hypothesis, in vivo exposure of low dose TCDD provokes dose and duration dependent toxic effects to key lysosomal enzymes and thereby causes cellular apoptotic changes. Three groups of female Swiss albino mice were subjected to two doses of TCDD (0.004 mg/kg bw/d, 0.04 mg/kg bw/d) for 2, 4 and 6 days of exposure durations. The results indicated significant exposure duration dependent effects of TCDD in mice liver cells. The results suggested that TCDD possibly induced an increase in intracellular ions or ROS which in turn altered different physiological activities by affecting different metabolic pathway of the liver cells. The altered functions of key lysosomal enzymes by TCDD may also evoke the process of cellular apoptosis.     

Effects of aging on resistance to Trichinella spiralis infection in rodents exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Immune function, including resistance to infection, decreases as humans and rodents age. We have shown that preinfection exposure of young (9-11 weeks) mice or rats to TCDD decreased resistance to Trichinella spiralis (Ts) infection, expressed as delayed onset or completion of parasite elimination and as increased muscle burdens of larvae. It has also been shown that aged mice express lower constitutive levels of resistance to Ts infection, compared to young adult animals. This study tested the hypothesis that the age-related decrease in constitutive levels of resistance to Ts infection exacerbates the decreased resistance to infection that follows TCDD exposure. This hypothesis addresses the concern that TCDD may pose a greater threat to the elderly than to the population at large. Animals were given a single oral dose of 1, 10, or 30 microg TCDD/kg, 7 days before infection. Eleven days later, young (approximately 10 weeks) control rodents had eliminated a greater proportion of the original parasite burden from the intestine than aged control animals. Nevertheless, parasite elimination was decreased by TCDD exposure only in young rodents. The effect of TCDD exposure on numbers of encysted larvae was evaluated only in rats. Increased larvae burdens occurred in young rats at 30 microg TCDD/kg and at 10 or 30 microg TCDD/kg in aged rats. Parasite-specific splenocyte and lymph node cell proliferation was suppressed following dioxin exposure in young mice; cells from aged mice were markedly less responsive to stimulation, yet less sensitive to TCDD exposure. The response to parasite antigens was not affected in aged rats exposed to TCDD, although elevated mitogen-driven B-cell proliferation was observed. These results indicate that age-related constitutive immunosuppression did not exacerbate TCDD-induced suppression of T-cell mediated adult parasite expulsion; rather, advanced age provided some degree of protection. On the other hand, a lower dose of TCDD was required in aged rats to suppress the combined humoral and cellular responses that limit the burden of encysted larvae, compared to young rats. These model-dependent results preclude acceptance or rejection of the tested hypothesis.